WHAT IS THE NAME OF THIS BOOK??? ITS DRIVING ME NUTS HOLY COW?

(note it's been years since i've read this book. I dont remember all the details.) basically this book is about two kids that wake up in their room one day, and they get up to say morning to their mother, but when they leave their room they see that the walls have been repainted and there's odd furniture now and they cannot find their mother. They search the house and yard but don't find her. They don't leave the yard because their mother strictly told them to never leave it without her. When they go back in the house they see two ghost children, who can also see them. They can't talk to each other, but they can communicate. Then the two original children also see the ghost children's mother, who is very mean. The two original kids try to help the ghost children hide and escape from the ghost mother, but it doesnt seem to work. Other stuff happens, and in the end, the two original children hear their mother come in the door. It turns out that the two original children had drowned in the lake in their backyard, and their mother, so grieved, had sold the house, but demanded that the new owners not change her children's rooms. Which is why their room was the same, even though the rest of the house had changed. The "ghost" family was actually just the new family that had moved into their house. The reason they finally found their mother is because she too had died.

I'm really if this doesnt make sense but it's been years since i've read this book.